How to use the flow rate converter
- Enter the flow rate in Value. The default is 10.
- Choose its unit in From, such as L/min or US gal/min (GPM).
- Choose the unit you want in To. The answer appears at once.
- Read the table below for all 13 units, or use the swap button to go the other way.
What it does and when to use it
A flow rate tells you how much volume passes a point in a given time. Different trades count it in their own units. Plumbers and pump sellers use L/min or GPM, water utilities and process plants use m³/h or m³/day, ventilation specs use CFM, and the oil industry uses barrels per day.
Typical tasks: checking that a pump rated in GPM can feed a system designed in L/min, comparing a kitchen extractor’s CFM with a ventilation rule written in m³/h, or estimating how long a tank takes to fill. For the tank, divide its volume by the flow (both in litres and minutes, say) to get the time; the volume converter and time converter help with mixed units.
How it works
Each unit is stored in cubic metres per second.
| Unit | m³/s |
|---|---|
| L/min | 0.001 ÷ 60 ≈ 0.0000166667 |
| m³/h | 1 ÷ 3,600 ≈ 0.000277778 |
| US gal/min | 0.003785411784 ÷ 60 ≈ 0.0000630902 |
| UK gal/min | 0.00454609 ÷ 60 ≈ 0.0000757682 |
| ft³/min (CFM) | 0.3048³ ÷ 60 ≈ 0.000471947 |
| oil barrels/day | 42 × 0.003785411784 ÷ 86,400 |
The tool multiplies by the From factor and divides by the To factor. All factors come from exact definitions: the US gallon is 231 cubic inches, the imperial gallon is 4.54609 litres, and the foot is 0.3048 m. NIST lists the same values for gallons per minute and cubic feet per minute.
Worked examples
A US pressure washer. 5 GPM = 18.92705892 L/min, or 1.1356235352 m³/h.
A range hood rated 400 CFM. That is 679.604318208 m³/h, or 188.77897728 L/s.
A small oil field. 1,000 barrels per day = 158.987294928 m³/day, about 110.4 L/min.
Limits and tips
- Rated and real flow differ. Pumps and fans give less flow against pipe friction or duct resistance. Look at the maker’s curve, not just the headline number.
- “Gallons” without a label almost always means US gallons on equipment sold in North America. Pick UK gal/min only when you know the figure is imperial.
- For the speed of a fluid in a pipe, divide the flow in m³/s by the pipe’s cross-section area in m²; then the speed converter gives other units.
Frequently asked questions
How many litres per minute is 1 GPM?
What does CFM measure?
Can I convert flow rate to kilograms per second?
How big is an oil barrel?
Is gas flow at different pressures handled?
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically — NIST, accessed 2026-10-08
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